Field of the Invention
The present invention relates to a booster unit for moving a vehicle on a slope and a method of controlling the booster unit, more particularly to a booster unit capable of easily moving a vehicle on a slope by a suitable release timing control for brake fluid pressure when moving the vehicle on the slope and a method of controlling the same.
Conventionally, booster units for moving vehicles on a slope are known, one of which is for example disclosed in Japanese Patent Disclosure No. 75162/1983.
The booster unit according to the prior art comprises an accelerator switch for detecting acceleration operation for the start of a vehicle, a vehicle tilt sensor for detecting the tilt of the vehicle in the direction of moving and an engine speed sensor, whereby an accelerator is operated when actual vehicle tilt angle is below a predetermined tilt angle value during running on a generally flat road, with a brake lock released. On the other hand, when the vehicle tilt angle becomes above the predetermined value, the release of the brake lock is delayed until the engine speed reaches a predetermined value.
In the booster unit according to the prior art, however, the release timing is controlled in accordance with the engine speed regardless of the clutch conditions. As a result, when the vehicle is in the clutch disengaged condition, or in the initial condition of the clutch engaged condition, the engine speed is increased due to engine idling and the brake fluid pressure often tends to be released with the result that the vehicle is moving back without obtaining a sufficient starting torque. Also, there occurs a problem that when the clutch is in a completely engaged condition, the moving torque is increased too much to suddently move the vehicle at the time when the engine speed reaches a predetermined value where the brake fluid pressure should be released.
In addition, the wear of the clutch causes the change in the clutch engaged position, thus imposing a problem that the release timing of the brake fluid pressure must be corrected in accordance with the change in the engaged position or disengaged position of the clutch.